Sharp bounds for the fractional chromatic number of high-girth d-degenerate graphs

Peter Allen, Abhishek Dhawan, Jonathan A. Noel

Allen, Dhawan and Noel prove that for every fixed girth g≥4 there are d-degenerate graphs of girth at least g with fractional chromatic number at least (1−o(1))d/log d as d grows. ChatGPT solved the authors’ optimization problem for the fractional clique function used in this lower-bound proof.

Sources for this record

What was already known

Martinsson and Steiner had established a constant-four scale for triangle-free d-degenerate graphs and conjectured the sharp leading constant one.

AI involvement AI-centered

ChatGPT 5.5 Pro determined the optimized fractional clique function from an objective posed by Allen, Dhawan and Noel. They developed the construction, proof strategy and final article.

The model solved a central function-shape optimization, while the authors supplied the random construction and strategy.

Importance Notable

The construction reaches the conjectured lower constant for arbitrarily large fixed girth.

Limitations

The authors designed the random construction and overall proof. Their separate upper-bound theorem is outside this AI assessment, and no completed check of the model’s optimization is documented.

Technical verification Reported

A written proof and author responsibility are available, but no completed check of the model optimization is documented.

Human understanding Full

The authors explain the function and how it drives the lower-bound argument.

Correction and publication history

2026-10-18 · publication

Only the model-assisted lower-bound function is assessed; the paper’s upper-bound proof is separate.

Read this published revision